The approaches described in this section are approaches that could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.
The flashes on many portable cameras can cause undesirable defects in captured images. One of the most common defects is a “Red-eye” phenomenon where a flash is reflected within a subject's eye and appears in a photograph as a red dot where the black pupil of the subject's eye would normally appear. The unnatural glowing red of an eye is due to internal reflections from the vascular membrane behind the retina, which is rich in blood vessels. This undesired defect is well understood to be caused in part by a small angle between the flash of the camera and the lens of the camera. Due to the miniaturization of cameras with integral flash capabilities, the phenomenon can be quite pronounced in many of today's smaller, portable cameras.
The red-eye defect can be minimized by causing the iris to reduce the opening of the pupil, such as with a “pre-flash,” which involves a flash or illumination of light shortly before a flash photograph is taken causing the iris to close. Unfortunately, the pre-flash occurs 0.2 to 0.6 seconds prior to the flash photograph, which is a readily discernible time period within the reaction time of a human subject. Consequently, the subject may believe the pre-flash is the actual photograph and be in a less than desirable position at the time of the actual photograph, or the subject might be informed of the photograph by the pre-flash, typically loosing any spontaneity of the subject that could be captured in the photograph. Therefore, the use of a pre-flash, while somewhat helpful in reducing the red-eye phenomenon, can negatively affect images in other ways.
With the advent of digital cameras and digital image software on computers, techniques for eliminating flash-induced eye defects by processing a captured image with microprocessor-based devices, either external to a camera or built into a camera, have become common place. Most of the algorithms executed by the microprocessor-based devices are quite rudimentary. For example, a common defect removal algorithm involves looking at a digital image for pixels within a color spectrum that form a shape within a range of shapes to identify defect candidates. Techniques exist for narrowing the color spectrum and narrowing the shape range that algorithms use to identify potential defects candidates, but those existing techniques are very limited, and in many cases, are as likely to cause a true-positive to be missed as they are to cause a false-positive to be avoided because such techniques do not account for the physiological variations in human eyes or the conditions under which the image was captured. Therefore, there exists in the art a need for improved flash-induced eye defect detection and correction algorithms.